The invention relates to a network station to be operated by a subscriber.
The telecommunication networks are nowadays still provided with both analog and digital terminals in the subscriber area. With analog operation, which is also referred to as the POTS mode (POTS=Plain Old Telephone Service), the analog terminal receives analog signals from an analog module in a switching center, and with digital operation, which is referred to as the ISDN mode (ISDN=Integrated Services Digital Network), the digital terminal receives digital signals from a digital module in the switching center. For the digital operation it is necessary to have an ISDN network terminator which is inserted between the digital terminal and the digital telephone.
It is an object of the invention to provide a network station which, in the event of a mode change in the switching center, enables operation both in the POTS mode and in the ISDN mode.
The object is achieved by a network station comprising a selector switch for coupling a switching center to a POTS or ISDN telephone which network station contains a detection circuit which, after being put into operation or after a mode change from the POTS mode to the ISDN mode, is provided for coupling the switching center to an ISDN network terminator and, in the event of a mode change from the ISDN mode to the POTS mode, for coupling the switching center to the POTS telephone by actuation of the selector switch.
After being put into operation, the network station couples the switching center to an ISDN telephone via a selector switch. The network station is put into operation, for example, after a network failure or after it has been built-in at a subscriber station. When the detection circuit recognizes that there is no ISDN mode available, the detection circuit controls the selector switch so that it couples the switching center to an analog or POTS telephone. The advantage of the measures according to the invention is that a change-over from the analog to the digital mode of operation can be effected practically in a remote controlled fashion by the switching center and, therefore, no service need to be rendered at the subscriber end.
An embodiment of the detection circuit comprises a rectifier coupled to the input terminals of the selector switch, a threshold detector, a first and a second pulse shaper circuit and a bistable relay. The threshold detector compares the signal produced by the rectifier to a threshold value and the first pulse shaper circuit generates an actuation signal for the bistable relay to change the selector switch from the POTS mode to the ISDN mode when the signal produced by the rectifier has reached the threshold value. The second pulse shaper circuit generates an actuation signal for the bistable relay to change the selector switch from the ISDN mode to the POTS mode when the ISDN network terminator cannot carry out an ISDN operation with the switching center.
The detection circuit further includes a timing element which is provided for delaying the generation of an actuation signal of the first pulse shaper circuit. This suppresses noise pulses and the AC signaling voltage in the signal arriving from the switching center.
A microprocessor coupled to the ISDN network terminator evaluates status messages of the ISDN network terminator. The second pulse shaper circuit generates the actuation signal for the bistable relay after the microprocessor has generated an excitation signal. The microprocessor generates an excitation signal when the microprocessor receives a message from the ISDN network terminator about the ISDN mode that cannot be effected.